Muscle contraction is initiated by a signal sent by the central nervous system through the release of __________.

Step-by-step solution

Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron. When the neural signal reaches the neuromuscular junction or motor end plate, it triggers the release of a neurotransmitter called acetylcholine. Acetylcholine binds to receptors on the sarcolemma, generating an action potential that spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm, thereby initiating muscle contraction. Answer: acetyl choline